1. Field of the Invention
This invention relates to the field of exhaust gas recirculation (EGR) recovery.
2. Description of the Related Art
There are competing controls at work with an exhaust gas recirculation (EGR) equipped engine. One is trying to keep the brake specific oxides of nitrogen (BSNOx) levels at the emission standard while the other is trying to maintain a drivable vehicle. EGR may be provided to an intake air charge to damp combustion temperatures, thus reducing the amount of BSNOx that is being produced. EGR, however, replaces some of the air in the intake charge, promoting smoke generation if the air-to-fuel ratio falls too far. Large amounts of smoke can occur with EGR application when the driver wants to quickly accelerate the vehicle. Under these conditions EGR flow may be suspended briefly while fuel is added and the turbocharger is used to accelerate the vehicle. Higher levels of BSNOx emissions, however, are produced while the EGR flow is suspended.
The BSNOx emission standard is based on a 20 minute driving cycle and contains numerous quick accelerations. The overall engine calibration may be lowered in order to make up for the higher level of BSNOx produced during rapid accelerations. Lowering the engine calibration continuously to make up for brief periods of higher BSNOx, however, hurts the steady state fuel economy.